Heart failure is a complex disease with many forms and causes. In general heart failure is defined as a condition where the cardiac output is not adequate to meet the metabolic needs of the body, either at rest or with exercise. Heart failure may be preceded by heart dysfunction, including, but not limited to ventricular dysfunction.
There are two forms of heart failure, one where the hearts ability to expel the blood is impaired (systolic heart failure), another where there is a defect in ventricular filling (diastolic heart failure). Each can occur in isolation or together.
Current treatments for heart failure are available to slow the progress of the disease but do not cure the disease. Despite all the current therapeutic options, studies show that more then half of heart failure patients die within 5 years of their diagnosis.
Accordingly it would be desirable to provide new and useful treatments for heart failure or other cardiac/cardiovascular disease.
Pacemakers have been useful where there are cardiac bradyarrhythmias. Defibrillators are primarily used to prevent sudden cardiac death and therefore have not improved the status of heart failure patients nor have they improved quality of life. Cardiac Resychronization Therapy devices (CRTs) have been useful or in patients with significant interventricular delay or in preventing cardiac tachyarrhythmias or sudden cardiac death (CRT-Ds). There are many heart failure patients who may not substantially benefit from one or more of these treatments or may not have an improved quality of life from such treatments. For example, CRTs have not been approved for patients with ejections fractions greater than 35% and thus are not available for diastolic heart failure patients who typically have ejection fractions greater than 50%, or for systolic patients with an ejection fraction greater than 35%. Some studies show diastolic heart failure to account for up to ⅓ of the patients presenting with heart failure. In addition, because the current treatments do not cure heart failure, additional treatment that may be used in combination with existing treatment may be beneficial to the patients.
Many of the drugs such as calcium channel blockers, beta blockers, ACE inhibitors, diuretics, nitrates have had varying degrees of effect on different manifestations of heart failure. However, not all are useful to treat all heart failure patients. Furthermore, due to side effects some patients withdraw from treatment. Pharmacological therapeutic approaches to diastolic heart failure currently recommend diuretics and nitrates while the efficacy is uncertain for all diastolic heart failure patients with calcium channel blockers, beta blockers, ACE inhibitors. Inotropic agents are not recommended for diastolic patients. Accordingly it would be desirable to provide treatment for heart failure that may be used alone or in combination with other heart failure treatments. It would also be desirable to provide alternative or supplementary treatment for diastolic heart failure patients.
Another cardiovascular condition that may exist with or without heart failure is hypertension. Hypertension is believed to worsen heart failure. It is also believed that hypertension may lead to diastolic heart failure. Studies have shown that treatment of hypertension reduces the incidence of heart failure by 30% to 50%. Accordingly it would be desirable to provide a treatment for hypertension.
In addition, a large percentage of heart failure patients also suffer from one or more forms of sleep apnea: obstructive sleep apnea or central sleep apnea, (each of which have significant clinical differences), or mixed apneas. These conditions are believed to worsen progression of heart failure. Obstructive sleep apnea is also believed to contribute to the development of heart failure, particularly through hypertension.
Oxygen desaturations at night, changes in intrathoracic pressure, and arousals may adversely effect cardiac function and eventually result in an imbalance between myocardial oxygen delivery and consumption. In heart failure patients with sleep apnea, there is believed to be an increased incidence of atrial fibrillation, ventricular arrhythmias and low left ventricular ejection fraction. Atrial fibrillation may be caused in part by increased right heart afterload due to hypoxic vasoconstriction which produces pulmonary hypertension. Periodic breathing such as Cheyne-Stokes associated with CSA, create wide fluctuations in intrathoracic pressure with a negative cardiovascular impact. Central sleep apnea sometimes goes undiagnosed in heart failure patients. The untreated central sleep apnea may trigger a negative chain of events that leads to worsening of heart failure.
Obstructive sleep apnea is believed to elicit a series of mechanical, hemodynamic, chemical, neural and inflammatory responses with adverse consequences for the cardiovascular system for example, as described in Sleep Apnea and Heart Failure Part I: Obstructive Sleep Apnea. Bradley, Douglas T, MD, Floras, John S., MD D Phil, Circulation Apr. 1, 2003. Many of these effects are believed to exacerbate conditions of heart failure. Among these responses, increases in blood pressure as well as increases in sympathetic activity are associated with obstructive apneas.
Accordingly it would be desirable to treat sleep apnea in heart failure to reduce the negative effects of the apnea on the patient's disease status.
CPAP is the most common treatment for obstructive sleep apnea and has been proposed for central sleep apnea. CPAP requires an external device and patient compliance. In addition, its cardiovascular effects are currently unclear and some researchers believe that it can exacerbate heart failure in some patients, particularly where positive forced pressure has a negative effect on a heart failure patient, such as, for example, in patients where a reduced ventricular filling would significantly reduce cardiac output. Diaphragm stimulation has been proposed to treat central sleep apnea by stimulating when apnea has occurred. However, the stimulation is provided after the apnea event has occurred rather than preventing the apnea event. Hypoglossal nerve stimulation has been proposed to treat obstructive sleep apnea by increasing patency in the upper airway to enable respiration. But it is believed would not provide additional benefit to heart failure patients other than that of treating the obstructive apnea.
It would accordingly be desirable to provide a treatment for sleep apnea that has a symbiotic therapeutic effect in treating heart failure or other cardiac/cardiovascular disease.
It would further be desirable to provide a treatment for heart failure patients with sleep apnea that provides a separate or additional function of treating heart failure.
Research has shown that voluntary control of breathing can improve cardiac disease, including hypertension and heart failure. It is believed that the reason for this is a biofeedback that exists between the cardiac and respiratory systems due to baroreceptor based reflexes, and also a common central nervous control. Biofeedback systems for breathing control have been provided. However, they require patient compliance and diligence. Furthermore, because they require patient compliance, the therapy can only occur during waking hours.